Abraham bar Chiyya

(c. 12th century)

Abraham bar Chiyya lived during the first part of the
12th century in Barcelona. He was a multi-talented rabbi.
He was a philosopher, astronomer, mathematician, surveyor, astrologer,
and interpreter, possessing exactly the skills needed by the conquering
Christian kings. He served as a court functionary and was also given
authority within the Jewish community.

Bar Chiyya's philosophic endeavors focused
on two different questions. He was interested
in how the world was created, and he was interested
in figuring out when the end of time would
take place. His book on the subject, Megillat
Ha-Megalleh was the first eschatological
book written by a European rabbi.
According to his calculations, the world would
be redeemed in 1383, and resurrection would
take place in 1448. He had a powerful influence
on subsequent scholars and astrologers.

Abraham bar Chiyya was the author of the
first major book of mathematics written in Hebrew.
He also sent a treatise to the Jews of France to help them with their measurements of fields.
He thus introduced Arabic trigonometry to
the West. This treatise was the first Hebrew
work to introduce the concept of pi and show how it could be used to find the
area of a circle.

Abraham bar Chiyya's astronomical works included a major work on the
earth's geography and a major treatise on intercalation. His computations
were considered authoritative.

Abraham bar Chiyya was a contemporary of Rabbi
Judah bar Barzillai, with whom he had
a public disagreement. Bar Chiyya wanted a
wedding postponed because the astrological
signs were not positive. Judah bar Barzillai
refused because he viewed astrology to be
illegal in Jewish
tradition. The two exchanged letters on
this topic.